As a method of measuring a density of poisonous material such as organic solvent vapor in a working environment and a dose of a substance to which a person is exposed in the working environment, there has been known a method using an absorbent such as activated carbon, so-called a solid material collecting method. Generally, following effects can be obtained with this solid material collecting method.
(1) Substantially 100% of organic solvent vapor or the like can be collected with an absorbent. PA0 (2) Time-weighted mean of density can be obtained. However with the direct collecting method, it is possible to measure only a transitional density. PA0 (3) As organic solvent vapor or the like can be condensed, it is possible to quantify the vapor or the like in a low density. And for this reason, a range in which the vapor or the like can be measured is very wide. PA0 (4) A method of gas chromatography (described as "GC" hereinafter) is used for quantifying the vapor or the like, so that even mixed gas or mixed vapor can be measured.
However, an absorbent used for the solid material collecting method has a limited capacity for absorbing a solid material. For this reason, when the collection is executed for a long period of time, poisonous substances pass through the absorbent. If any poisonous substances pass therethrough, the measurement will become incorrect.
For this reason, many of commercial solid material collectors have such configuration that adsorbents are packed therein in two layers, in an upstream side as well as in a downstream side of the device. The absorbent in the upstream side thereof is used as a sample to be analyzed by means of the GC. The absorbent in the downstream side thereof is used for checking whether any of the substances has passed through the absorbent or not.
With this configuration, the material to be measured passing through the absorbent in the upstream side is collected by the absorbent positioned in the downstream side. Accordingly, if any material to be measured is detected in the absorbent in the downstream side by analyzing it, the fact indicates that the material passed through the absorbent in the upstream side. So, effectiveness of the measurement is determined according to a quantity of the material having passed through the absorbent in the upstream side. If the quantity is too large, a result of the measurement is not reliable, which indicates that the measurement is a waste of time.
FIG. 24 shows a partially broken perspective view of a solid material collector 900 based on the conventional technology. An absorbent 903 in the downstream side and that 902 in the upstream side thereof are serially packed in a collecting tube 901. Activated carbon is used for the absorbents 902 and 903. A duct 904 comes out from an edge section of the collecting tube 901. A small size electric pump 905 is connected to the edge section of this duct 904. The reference numeral 906 indicates a clip for attaching this device to a user. When the pump 905 is driven, environmental air is introduced into the collecting tube 901 through an opening edge thereof. Organic solvent contained in the environmental air is collected by the absorbent 902. The air passing through the adsorbents 902 and 903 passes through the duct 904 to be discharged from an air outlet port of the pump 905.
FIG. 25 is an explanatory view showing how an operator wears the solid material collector 900. The collecting tube 901 is attached with a clip 906 onto a shoulder portion of the clothes which a user M wears. The pump 905 is fixed to a belt or the similar position of the user M. The user M works with this solid material collector 900 on. When the work is finished, the absorbent 902 in the upstream side as well as that 903 in the downstream side are taken out from the collector. Then, the absorbent 902 in the upstream side is analyzed with the GC to quantify the collected material to be measured. The absorbent 903 in the downstream side is also analyzed. If any material to be measured is detected from the absorbent 903 in the downstream side, it is understood that the material passed through the absorbent 902 in the upstream side. When a quantity of the detected material to be measured is larger than a specified quantity, a density of the material in the environment or a dose of the material to which a person is exposed can not accurately be measured. Accordingly, it can be determined that this measurement is invalid.
However, in the solid material collector 900 described above, effectiveness of the measurement can not be determined before the collecting work is finished. For this reason, the measurement can not always accurately be made. And also, the absorbent 902 is sometimes wasted thereby.
There has also been known a method in which a period of time from the beginning of the measurement until the absorbent 902 is about to be passed through by the material to be measured under a constant gas density is previously measured and the measurement is stopped just before passage of the previously determined period of time. However, a gas density in the working environment generally changes from time to time and from place to place. Also a user tends to move around in the working environment. And for this reason, the user can not accurately estimate the period of time until a material to be measured starts passing through the absorbent in the upstream side.
It is also conceivable to make a capacity of an absorbent larger. However, when the capacity is made larger, a capacity of a pump is required to be made larger proportionately. For this reason, a size of the pump becomes large, which lowers portability of the solid material collector.
By the way, the absorbent described above is also used for a gas mask or an air line mask used in cases of spraying agricultural chemicals, handling drugs, painting, or cleaning or the like, which is different from the purpose of the absorbent when used for measuring a density of poisonous materials in a working environment or a dose of the substances to which a person is exposed. In these cases, the passage of the poisonous material through the absorbent becomes an extremely serious matter. If the determination that the passage of a poisonous material through the absorbent has been generated is made after it actually occurred, sometimes it is too late.
Currently, there has been employed a method in which a period of working time (a period of time before passage of a poisonous material through an absorbent occurs) is computed from a gas density in the working environment and the work is stopped before the passage actually occurs. However, there is the fear that the period of working time is reduced because the gas density in the working environment is not uniform. Especially, in a case where fatally poisonous materials such as chemical weapons or the like are handled, it may bring about a serious danger to an operator.